Equine neonates are susceptible to a wide variety of pathogens because of their naïve immune systems. As a result, sepsis in foals is a matter of concern to the equine industry.1 Maria Julia Felippe, Med.Vet., MS, PhD, DACVIM, associate professor of large animal medicine at Cornell University's Equine Immunology Lab, is part of a Cornell group studying the development of the foal's immune system. The following discussion outlines several critical aspects of their work that's expanding our understanding of immunity.

Immunity basics

GETTY IMAGES/RICHARD LOADER

Foals begin to develop their innate and adaptive immune functions partially during gestation but more significantly after birth when exposed to environmental organisms.1

Colostrum is an essential source of immune components for newborn foals, the most important of which is IgG. Inadequate IgG absorption results in a partial or total failure to transfer immunoglobulins to the newborn, causing increased susceptibility to infectious diseases. Even with sufficient IgG, foals are susceptible to certain pathogens that rarely affect adult horses, such as Rhodococcus equi.

Transferring proinflammatory cytokines to the foal

A group of Cornell researchers that included Felippe found that "the transfer of cytokines in colostrum to equine neonates could have immunomodulatory effects and help with protection early in life. Perhaps foals with inadequate colostral ingestion and absorption may be more susceptible to infectious diseases not only because of the critical concentrations of IgG but also because of low proinflammatory cytokine transfer from colostrum—both important to help fight off pathogens before competence of their own immune systems are developed."1

This research determined that "serum TNF-alpha concentrations were high in postsuckle samples, though essentially undetectable in presuckle samples, as the TNF-alpha concentration in postsuckle serum predicted the concentration in colostrum."1 The data suggested that "TNF-alpha is transferred to the foal via colostrum absorption and may play a role in early immunity. It is possible that the transfer of proinflammatory cytokines in colostrum helps with immune alertness and protection before the foal can efficiently elaborate an immune response. TNF-alpha has a key role in sepsis due to its potent proinflammatory properties."1

"It's possible that intake and absorption of proinflammatory cytokines in the colostrum might help," says Felippe. "In the manuscript, we cited previous work done in calves where they found that when you give IL-1 orally, it did have an immunomodulatory effect. If foals are drinking colostrum that contain cytokines, these cytokines are going to be absorbed, either to work systemically or locally in the gastrointestinal tract, and have an immunomodulatory effect. By analogy with what's been done in calves, it's very possible."

Felippe's team specifically looked into TNF-alpha, but other cytokines could be transferred via the colostrum. Some have suggested that IL-6 is one of them, though it has not been studied as systemically. "Maybe other anti-inflammatory cytokines, such as IL-10 could be transferred as well," Felippe says. "But we still need to learn how they are transferred through colostrum and what the effects are."

The potential for the immunomodulatory effects for cytokines is speculation at this point, but it may aid the neonate's immune response. "One answer that we don't know is the magnitude of an effect," Felippe says. "Is it dose-dependent? Do you need a lot of TNF-alpha to get an effect or a little bit? That is really an open question.